A family physician's guide to monitoring methotrexate.

Methotrexate has a long history of use in the treatment of various immunologic diseases, including rheumatoid arthritis and psoriasis. Although the drug is usually prescribed by a subspecialist, a family physician may assume responsibility for monitoring methotrexate therapy. Major toxic effects, such as hepatic, pulmonary, renal and bone marrow abnormalities, require careful monitoring. Minor toxic effects, such as stomatitis, malaise, nausea, diarrhea, headaches and mild alopecia, are common but respond to folate supplementation. Methotrexate is administered once weekly as a single dose or in divided doses given over a 24-hour period. To reduce the incidence of major toxic effects, methotrexate should never be given in daily doses. Relative contraindications include renal dysfunction, liver disease, active infectious disease and excessive alcohol consumption. Both women and men of reproductive age should use birth control during methotrexate therapy. Potential drug interactions include salicylates and nonsteroidal anti-inflammatory drugs, which are both commonly used in patients with rheumatoid arthritis or psoriasis. A premethotrexate evaluation is important to ensure proper patient selection for this effective but potentially toxic drug.